Can Cardinal tetra Live With Rummy-nose tetra?

Both are South American characins of the same temperament, and the rummy nose is explicitly recommended alongside other characins of this kind. The cardinal is peaceful and suits the same community. Neither crowds the other.

The water matches better than in most tetra pairings: 24 to 27 °C and pH 5.5 to 7 work for both, warm and soft, which is what the cardinal in particular wants.

Numbers matter more here than usual. The rummy nose shoals more tightly than almost any small tetra and fares badly in insufficient numbers, so buy at least 10 and preferably more; cardinals also do best in groups of 10 or more. Fish kept in short numbers become stressed and lose colour, which is the first thing you will notice. Two shoals of that size want about 80 litres rather than a 54 litre base, with driftwood, leaf litter and dim light.